The present invention relates generally to fluid pressure indicating instruments and more particularly to pressure gauges for measuring the pressure of fluids which, if used in ordinary type gauges, would be injurious to the reliable operation of the working parts of the instrument.
In using instruments such as, for example, pressure gauges, indicators, pressure transmitters and the like, it is often desirable to isolate the instrument from over pressure, corrosion, freezing, or the plugging of the instrument by sediment or the like suspended in or carried by the pressurized fluid. In the past, guard devices of the kind wherein a pressure sensitive diaphragm is interposed between the source of pressure and a liquid for transmitting motion from the diaphragm to the pressure responsive element of the instrument have been used to overcome the above mentioned problems. U.S. Pat. No. 3,202,063 to Bissell et al discloses, for example, "a guard device such that the pressure instrument may be disconnected from the top member of the casing while the diaphragm is exposed to the source of pressure. . ." Also, U.S. Pat. No. 2,568,238 to LeVan discloses, for example, "A fluid pressure-indicating instrument of the kind mentioned wherein the edge of the metal diaphragm is soldered to a seat formed on the removable structural unit, and is also forcibly held on that seat independently of the soldering by clamping means when the instrument is assembled."
When a seal assembly is used in conjuction with a gauge that is fluid filled, the fluid has to be carefully inserted into the gauge after the seal assembly has been attached to the inlet of the gauge. This care is required in order that no air bubbles will be present in the liquid to cause inaccuracies in the functioning of the gauge. Therefore, it is important that the diaphragm be carefully sealed in the seal assembly before the oil is placed into the gauge and the adjoining seal assembly. In the past, two general sealing techniques have been used in the assemblies. Either the diaphragm was loosely placed between two members of the seal assembly and clamped between the members to sealingly engage the edges of the diaphragm or the diaphragm was soldered onto the portion of the assembly which was connected to the gauge. In the latter case, which is illustrated and described in the aforementioned patents, there is an advantage in that the portion of the assembly attached to the gauge may be removed for cleaning the diaphragm, and the like, without losing the fluid in the gauge. However, soldering or welding the diaphragm onto the assembly causes problems such as stressing and thereby weakening the diaphragm which is generally very thin, being restricted to a diaphragm having a metal outer periphery capable of being welded or soldered, forming a permanent assembly which is difficult to repair, and requiring a relatively complicated manufacturing procedure which may be expensive. It has been known to clamp a diaphragm into a housing by a flange as illustrated in U.S. Pat. No. 2,220,902 to Hastings et al but there is no teaching of clamping a diaphragm in an environment as provided in the present invention.